The overall objective of the proposed studies is to use experimental genetic approaches that are available in the mouse to identify genetic, and thus molecular, elements that underlie the control of sleep and wakefulness. To reach this objective, two general strategies will be taken. One strategy will involve the use of the recently discovered Click gene which, when mutated, affects the period and expression of the circadian clock underlying the rest-activity and sleep-wake cycles and possibly also the total amount of sleep in mice. Clock represents the first mammalian circadian clock mutation show to affect sleep. Sleep EEG activity will be recorded from mice of three different Click genotypes (wild-type, heterozygotes, and homozygotes) under both entrained and free- running conditions, as well as following periods of sleep deprivation, to determine how this gene regulates both the circadian and homeostatic processes underlying sleep and wakefulness, as well as the interactions between the sleep and circadian systems. The second strategy will involve the use of two different forward genetic approaches to find new genes that are involved in sleep regulation. One approach will use inbred strains of mice to determine the effects of different genetic backgrounds on sleep, and through the use of Quantitative Trait Loci (QTL) analysis identify linkage of chromosomal regions with sleep EEG phenotypes. Isolating chromosomal regions containing candidate sleep regulatory loci on a congenic strain background will allow the effects of each locus to be tested individually and will provide specific regions to be targeted for genetic mapping and gene identification. The second forward genetic strategy will utilize a chemical mutagenesis screen, successfully used to identify Clock, to create mutant animals with an altered phenotypic response of recovery sleep following sleep deprivation. Animals showing an unusual recovery time will be bred and their offspring used to completely characterize the phenotype and genotype of the mutation. Ultimately, positional cloning techniques will be used to identify the mutated genes underlying the homeostatic control of sleep. Determining the molecular mechanisms by which Clock (and its protein product) regulates both the timing and the need for sleep, and the identification of new genes involved in sleep regulation, will provide new information on the genetic and molecular control of sleep. Such information is expected to lead to new treatments for sleep disorders, mental and physical disorders associated with sleep-wake abnormalities, as well as for strategies to influence human fatigue and alertness.